Tocopherol compounds occur in many vegetable and animal oils and are also referred to as vitamin E. The vitamin E relates to the physiological effect of these food ingredients.
There are 8 naturally occurring substances with vitamin E activity. They are derivatives of 6-chromanol and belong to two groups of compounds. The first group is derived from tocol and carries a saturated isoprenoidal side chain containing 16 carbon atoms. This group includes alpha-, beta-, gamma-, and delta-tocopherol. The compounds differ in their degree of methylation at the benzene ring of the tocol. Alpha-tocopherol is the substance with the strongest biological vitamin E effect and the greatest technical and economical importance. It is the dominant tocopherol in human and animal tissue.
The second group of substances with vitamin E activity are the derivatives of tocotrienol. They differ from the other tocopherol homologs in the unsaturated isoprenoidal side chain containing 16 carbon atoms. The naturally occurring tocoenols also show vitamin E activity and are normally isolated from their natural sources together with the saturated tocopherol homologs in the recovery of vitamin E. In the context of the present invention, the name "tocopherol" is also intended to encompass these tocopherol homologs, i.e. tocopherol are found in vegetable oils, such as wheat-germ oil, corn oil, soybean oil and palm kernel oil. However, tocopherol is also found in other vegetable oils, for example in safflower oil, peanut oil, cottonseed oil, sunflower oil, rapeseed oil, palm oil and other vegetable oils.
The natural plant oils contain only small quantities of tocopherol. Concentration is undesirable for commercial applications. In addition, impurities are supposed to be removed to enhance the antioxidizing effect and vitamin E activity. Accordingly, the most important natural sources of tocopherol are not the vegetable oils themselves, but rather the steam distillates--also know as steamer distillates--obtained in the deodorization of vegetable and animal oils. Although the tocopherols are obtained in concentrated form, they are mixed with sterol and sterol esters, free fatty acids and triglycerides. The distillate from the deodorization of soybean oil is particularly interesting. The particular suitability of soybean oil as a source of tocopherols is mentioned, for example, in Fat Sci. Techol., Vol. 91, 1989, pages 39 and 41 in a comparison of the deodorization distillates 25 of soybean oil and rapeseed oil. The soybean oil steamer distillate contains approximately 10 % (maximum) by weight mixed tocopherols and the same amount of sterols which are predominantly present in their ester form.
There are various known processes for the concentration of tocopherol, namely esterification, saponification and fractional extraction. Thus, according to DE 31 26 110 A1, tocopherol concentrates are obtained from secondary products of the deodorization of oils and fats by esterification of the free fatty acids present therein by addition of an alcohol or by removal of the free fatty acids from the distillates by distillation, after which these products are subjected to hydrogenation and subsequently to solvent fractionation to extract the tocopherols. Another process for concentrating tocopherol is known from the same document. In this process, the deodorization distillates are subjected to transesterification with methanol and the fatty acid methyl esters are distilled off. The residue is concentrated by molecular distillation.
In another process known from EP 171 009 A2, the tocopherol-containing material is contacted with a sufficient quantity of a polar organic solvent which dissolves the tocopherols, but not the impurities. The polar phase enriched with tocopherol is separated off and the tocopherol is recovered therefrom.
It is also known that the tocopherols can be separated by adsorption onto basic anion exchangers. This variant is possible if the mixture contains little, if any, fatty acid. The sterols, glycerides and other neutral or basic substances are not adsorbed (Ulmanns Enzyklopadie der Technischen Chemie, 4th Edition, Vol. 23, 1984, page 645).
It is also known that sterols can be separated from tocopherols by fractional crystallization after concentration. In this process, tocopherol passes into solution and sterol crystallizes out. Tocopherol and sterol can also be separated by distillation, except that in this case the sterol is at least partly destroyed. Accordingly, two useful products are obtained after the separation of tocopherol and sterol.
Known processes for the recovery of tocopherol and, optionally, sterol are attended by various disadvantages.
The extraction processes often have to be adapted to the starting mixture because the impurities present therein have a considerable bearing on extraction, and the desired useful products, tocopherol and sterol, do not always pass into the desired phase with the same extraction process and different starting mixtures. In addition, known extraction processes use physiologically unsafe solvents.
Ion exchangers have a specific effect on the starting material, required thorough preliminary purification of the mixture and do not allow tocopherol and sterol to be simultaneously concentrated.
In a variant described in DE 31 26 110 A1, tocopherol is subjected to molecular distillation or to steam distillation after esterification of the free acids with polyhydric alcohols in order to obtain a distillate having a high tocopherol content. However, the process step of molecular distillation is uneconomical on an industrial scale while steam distillation involves exposure to relatively high temperatures which at least partly destroys the sterols. In the latter case, therefore, only the thermally more stable tocopherol can be obtained in high yields.
Accordingly, the problem addressed by the present invention was to provide a process for the recovery of tocopherol and, optionally, sterol which would be applicable to many different starting mixtures and which would not use any toxicological or ecologically unsafe solvents, would not involve exposure to high temperatures, would give high yields and would be economically workable on an industrial scale. In addition, the simultaneous recovery of tocopherol and sterol would be possible.